1. Field of the Invention
The present invention relates to white stable graft polymer dispersions and polyurethanes prepared therefrom. More particularly, the invention relates to graft polymer dispersions prepared by the improved continuous process employing in situ free radical polymerization of an ethylenically unsaturated monomer or monomers in a polyol mixture containing from about 0.001 to 0.09 mole of induced unsaturation per mole of polyol mixture and further employing an effective amount of a chain transfer agent.
2. Description of the Prior Art
The prior art, as evidenced by U.S. Pat. Nos. 3,652,658; 3,875,258; 3,950,317, 4,137,396, and U.S. Re. Pat. Nos. 28,715 and 29,014 teach the preparation of graft polymer dispersions which are useful in the preparation of polyurethanes by the polymerization of ethylenically unsaturated monomers in the presence of polyols. The above patents disclose various methods of preparing graft polyol dispersions. U.S. Pat. No. 3,953,393 teaches the preparation of graft copolymer dispersions by employing alkylmercaptan chain transfer agents at concentrations from 0.1 to 2 percent by weight based on the weight of vinyl monomer. None of the prior art reveals an awareness of the desirability of conducting a continuous polymerization procedure to prepare graft polymer dispersions with uniform product viscosity employing unsaturation levels of from about 0.001 to 0.09 in the presence of a chain transfer agent. These products are employed to produce polyurethane foams having improved flame retardancy.